Tài liệu Điện thoại di động mạng lưới Radio P16 ppt

16
The Future is Wireless
16.1 A Typical Day in the Year 2000
Joe Mobilus is a manager with a haulage firm in a city 100 km away from his
home town; his wife Sue is a nurse at the local hospital. Their son Tom and
daughter Ann are still at school.
06:30 The central alarm system wakes Joe and Sue in line with their weekly
schedule.
07:00 Joe uses his TETRA terminal to access his firm’s central computer to
see if there have been any changes to his diary.
07:15 Joe leaves his house and using his cellular phone in the car calls the
traffic service to find out about current traffic conditions.
07:30 Tom, who is finishing school this year and wants to become a stock-
broker, calls up a stock market service on the Internet to have the share
prices from New York conveyed over satellite. Then, together with his
sister, he leaves to go to school. The Mobilus household is linked to the
PSTN/ISDN over an RLL system.
08:00 Sue’s cordless DECT telephone rings while Sue is in the bath. Her
mother informs her that she has to postpone the joint dinner that was
planned for that evening.
08:10 Sue informs Joe accordingly, over a pager or the GSM short-message
service.
08:15 Joe’s car breaks down as he is driving to work. He activates the auto-
matic emergency service for his car to call for help with a puncture. To
do so, he uses a TETRA service or GSM-SMS.
08:20 Because Joe is not sure whether he will make it to the office on time,
he sends his secretary an e-mail from his mobile data terminal with the
message that she should change his 9 o’clock appointment to a later
time. This message is served by GPRS, a non-transparent GSM data
service.
Mobile Radio Networks: Networking and Protocols. Bernhard H. Walke

Copyright © 1999 John Wiley & Sons Ltd
ISBNs: 0-471-97595-8 (Hardback); 0-470-84193-1 (Electronic)
806 16 The Future is Wireless
10:00 Joe has arrived in his office, where he receives a message that a client’s
warehouse flooded because of heavy rain during the night and that the
goods being delivered should be diverted to a different address.
10:05 The firm’s TETRA system enables Joe to make a group call to the
vehicles that are just on their way to the warehouse to notify them of
the new address.
11:00 A customer order requires Joe to spend a long time working closely
with Mr. Jones, another employee of the firm, who has his workstation
on another floor of the building. To save time, Mr. Jones has his work-
station transferred next to Joe’s. This can be done with no problems,
because the company has installed a HIPERLAN.
13:00 Sue, who has been working in the hospital for four hours, is just looking
after the patient in room 8 when she is paged over ERMES. The ERMES
terminal indicates that she is urgently needed in casualty admissions.
14:00 Joe has to talk to several colleagues jointly at the branch in Russia
about a decision concerning a cooperation agreement with a Russian
haulage company. He is able to reach them easily over the satellite radio
system IRIDIUM, but video conferencing is unfortunately not available.
15:00 Tom is called at home by a school friend. Because the friend was
ill, he was unable to attend classes today. He asks Tom to send him
the homework that was handed out in maths class today. Using the
fax machine connected to the DECT system, Tom is able to send the
information that was requested.
17:00 Ann, who is out shopping with her friend Jane, finds a nice shirt that
she wants to give her father for his birthday. Because she is not sure
which size to take, she goes to a pedestrian zone to call up her mother
using her DECT handset over a Telepoint service.

18:00 On the way home, Mr. Mobilus is informed over his cellular phone that
he has to visit a customer in Rome the next day. He is able to book his
air tickets and hotel reservations through a travel service from his car.
19:30 After an evening meal with his family, Joe arranges for the data he
needs from his firm for his appointment in Rome to be displayed on his
GPRS/GSM data terminal so he can have it printed out.
16.2 Wireless Communication in the Year 2005
Instead of having many different mobile radio systems and the associated
terminals, each modern user will have a software radio that, using the software-
defined configuration of the mobile terminal, adapts to the grade of service
16.3 Closing Remarks 807
of the radio interface, depending on the service and the location, and largely
makes decisions independently.
Because of the flexibility that this allows the user in selecting services,
the mobile network operators have entered into a price war and are offering
confusing, particularly reasonable rates supposedly restricted to certain user
groups. Modern users have a program installed within their terminal that
always selects the best rate specific to the current receive situation and to
the service to ensure that the software radio is switched to the corresponding
mode and the most favourable mobile radio service is being used.
UMTS-based PLMNs have been established, but are still available only in
highly crowded areas. The main mobile radio service in the large areas is still
served by second-generation systems like GSM.
There is no longer a restriction to narrowband services in hot communi-
cations traffic spots (like airports, sports arenas, fairs, etc.), because even
broadband (ATM- and IP-based) services are now available as wireless ser-
vices at broadband terminals. However, the costs for these services are still
so high that only business users can take advantage of them and afford the
appropriate terminals.
Since the narrowband telecommunications services of the fixed network

(telephony and data) have already been widely introduced over the Internet
and have bearable real-time characteristics, the packet-based GPRS speech
transmission is being extensively used for mobile calls because it is less ex-
pensive than the standard GSM telephone service. The GPRS has also been
adopted by the UMTS.
All mobile radio services have fallen dramatically in cost of usage and are
at almost the same cost levels as the corresponding fixed network services,
which are much lower in prize than in the late 1990s.
16.3 Closing Remarks
Our society is being characterized by increasing individual mobility and the
growing need for an exchange of information.
To be successful in domestic and international markets in the future, com-
panies and their employees inevitably have to be contactable at all times,
wherever they are and with the greatest confidentiality, and also have to have
access to the most up-to-date information.
The more mobile employees of a company are, the more difficult it is for
them to be reached and to have access to important information early enough
unless they use mobile radio services. Because of the variety of application
areas they are used in, mobile radio systems are also becoming increasingly im-
portant for private use. Thus newest-generation mobile radio systems, which
have established themselves in the commercial world, will become increasingly
cheaper through mass production, and therefore will appeal to an ever-growing
group of customers.
808 16 The Future is Wireless
The advantages of mobile radio systems and the evident trend towards uni-
versal systems in the future, which enable parallel transmission of voice, text,
data and images over one connection, thus allowing multimedia information
exchange based on UMTS and IMT 2000, will lead to a rapid increase in the
number of mobile radio users.
Third-generation systems will combine radio-based and fixed networks into

a standard architecture. This kind of network will consist of public and pri-
vate terrestrial components, as well as ground or space components from
radio-based networks combined in a way that a subscriber can use a stan-
dard terminal, the so-called Personal Communicator, to take advantage of
all the services offered by all networks available today and those that will be
operating in the next few years.
There is no conclusive response to the question repeatedly being discussed
in the media about possible repercussions to health arising from cellular tele-
phone use. Intensive studies are being conducted today on the biological
effects of electromagnetic radiation in the mobile radio area in order to define
meaningful limit values for acceptable radiation levels.
Because they are almost always physically separate, fixed radio facilities for
mobile telephone systems are only playing a minor role as potential sources
of danger due to electrosmog. Mobile equipment with integrated transmit-
ting antennas that radiate high-frequency waves near the head warrant more
concern. Most of the absorbed energy is converted into heat, and increases
the temperature of the body. In tests carried out on animals and simulated
human heads it has been determined that the metabolism, the nervous sys-
tem and behaviour can be affected even with an additional temperature rise
of 1 .
The World Health Organization and the national offices for radiation pro-
tection of many countries therefore recommend threshold values for the spe-
cific absorption and maximum power output (EIRP) of transmitting facilities
that are not to be exceeded, along with guidelines on the minimum permitted
distance between equipment or its antennas and a person’s body. Besides
the thermal effect of electromagnetic radiation, non-thermal effects can also
occur. These have been investigated for more than a decade, but there are
still no definitive statements about possible impacts of mobile radio waves on
humans.
The results of further scientific studies will influence the development and

suitable protective measures as well as the acceptance of mobile radio systems.
There is sufficient experience with human exposure to sources of danger, e.g.,
from cars and with electrical power.
Even if future research results point to a calculable danger from electrosmog
due to handset use, this will hardly have any impact on acceptance. The
danger-to-use consideration of individual mobile radio users will probably be
similar to what happened with the use of cars and electricity.